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大兴安岭地区显生宙花岗岩分布广泛,但区内中生代花岗岩的研究相对薄弱.通过对大兴安岭中段扎兰屯以西的毕家店岩体和神山岩体进行年代学和地球化学研究,探讨了本区早白垩世花岗岩的成因及构造背景.其中毕家店岩体主要由正长花岗岩和花岗斑岩组成,神山岩体主要由碱长花岗岩组成.毕家店岩体的锆石U-Pb年龄为136±3 Ma、139.5±0.9 Ma和128.1±0.8 Ma,神山岩体为119.3±0.8 Ma,均形成于早白垩世.地球化学特征上,两岩体均呈现高硅、低钙、富碱、Eu负异常等特征,亏损Nb、Ta,富集Rb、Th和U,属于弱过铝质高钾钙碱性系列,为岩浆演化晚期的高分异I型花岗岩.两岩体具有活动大陆边缘构造属性,结合大兴安岭地区同时期I型、A型花岗岩特征,认为早白垩世花岗质岩石的形成与太平洋板块俯冲背景下的拆沉作用密切相关.
The Phanerozoic granite is widely distributed in the Greater Hinggan Mountains, but the study of the Mesozoic granites in the area is relatively weak.Based on the geochronology and geochemistry of the Bijiandian and the magmatic rocks in the west of Zhalantun in the middle section of the Greater Xing’an Mountains, The genesis and tectonic setting of the Cretaceous granites.The Bijiadian rock mass is mainly composed of orthoclase granites and granite porphyries, and the magmatic rocks are mainly composed of alkali-bearing granite.The zircon U-Pb ages of the Bijiandian granite are 136 ± 3 Ma, 139.5 ± 0.9 Ma and 128.1 ± 0.8 Ma, respectively, and the Shenshan granite was 119.3 ± 0.8 Ma, both of which formed in the Early Cretaceous.On the geochemical characteristics, the two rocks show high silicon, low calcium, Eu negative anomaly and other features, depletion of Nb, Ta, enrichment of Rb, Th and U, belong to the weak permanganate high-K calc-alkaline series, for the late magmatic evolution of high I-type granite.The two continental bodies with active continental margin According to the characteristics of the conglomerate type I and type A granites in the Greater Hinggan Mountains, the formation of granitic rocks in the Early Cretaceous is considered to be closely related to the detachment effect under the Pacific plate subduction.